Circuit and starting switch for electric discharge devices



Nov. 16, 1954 C. H. WALKER ET AL CIRCUIT AND STARTING SWITCH FORELECTRIC DISCHARGE DEVICES Filed Feb 12, 1949 IIWVGYTbOTSI Cyril H.WaLker,

Fvederick E. La lge.

by (fizz. JCS

Their" Ai: omeg.

United States PatentO CIRCUIT AND STARTING SWITCH. FORKELECTRICDISCHARGE DEVICES:

Cyril Hubert Walker and ,Frederick. Edmund Large, .Rugby, England,assignors to. General ElectricCompany a, corporation of'New YorkApplication February lZ, 1949, Serial No. 76,165

. Claims priority, application. Great Britain April 8, 1948.

8 Claims. (CL 315.-10;,0)

This invention relates to the starting and operating of electricdischarge lamps.

'Electric dischargelamps of the low pressure type such, for example, asfluorescent lamps in which the predominantly ultraviolet radiation fromthe dischargeis converted into visiblelight by means of aluminescentmaterialon the interior of the envelope of the device, generally requirerelatively complex circuits for their starting and operation. This isdue to the fact that it is usually'necessary to preheat the electrodesto an electron-emitting temperature prior to the application of theoperating voltage between the electrodes.

In order to control the supply of preheating current to the electrode,use has generally been made of a thermostatic starter switch, thecontacts of which are arranged, when the source of supply voltageisconnected to the lamp, to connect the electrodes in a series circuit tothe source, whereby to supply heating current to the electrodes, thethermostatic switch being so constructed that after a predetermined timeperiod its contacts open, thereby interrupting the series circuitthrough the'lamp electrodes. As a result of the presence inv series withthe lamp of the inductance necessary for stabilizing the discharge, .avoltage pulse is impressed between the electrodes when the contacts ofthe thermostatic switchopen, whereby the discharge is initiated betweenthepreheated electrodes.

Two types of thermostatic switch have generally'been employed. Inonetype, commonly known as a thermal switch, the contacts are normallyclosed and'are arranged to.be opened by distortion of the bimetalelement of the switch when heated by a heating, element connected inseries in the circuit. supplying, the discharge current of the lamp.Whenvoltage is first applied to the. lamp circuit, current flowsthroughthe series circuitincluding the heating element of the thermostaticswitch, and vthe electrodes of the lamp causing them to heat up and atthe endof the preheatingperiod' the contacts ofthe thermostatic switchopenand the discharge between thevpreheated electrodes is initiated.Thereafter: the discharge currentflowing through the heating element ofthe switch is suflicient to maintain its contacts open, andonlyifthedischarge ceases by reason of the supply beingswitched off? or otherwisedo the contacts of the switch reclose ready for a further startingoperation.

In another well-known arrangement, the starting switch is of the glowdischarge type, the contacts beingnormally open and arranged, whenclosed, to complete the preheating circuit for the lamp electrodes.When-the supply isfirst connected to the lamp, aglowdischarge appearsbetween the contacts ofthe switch and, aftera predetermined period,distortion of the bimetal contact due to the heat of the glowdischargecauses the contacts to close, completing thepreheatingcircuit'for thelarnp electrodes. On closure of the contacts,however, the glow discharge ceases by virtue of' there being nopotential available betweenithe electrodesofthe switchto maintain it andthe contacts reopen after a time periodsufiicient to preheat the lampelectrodes to a desired electron emitting temperature. Thereafter, thevoltage, drop between the lamp electrodes is insuflicient to maintain aglow discharge between the contacts of the starter switch and only. ifthe discharge ceases vwith the lamp connected to the supply voltage willthe starting process described above recommence.

Itis an object of the present inventionto providean improvedformof=glow'discharge switchand of starting- '2 and operating circuitarrangement employingsame for electric discharge lamps of the kind,set-forth above.

'Other objects and advantages of our invention will appear from thefollowing description of. species thereof.

In the accompanying drawing, which illustrates the manner in which theinvention may be carried into effect, Fig. 1 shows, diagrammatically,one improved formof glow discharge starter switch employed; Fig. 2 is acircuit diagram illustrating the improved starting and operating circuitusing the starter switch of Fig. l; and Figs. 3 and 4 are two furtherforms of starter switch.

In accordance with one aspect of the invention, a glow dischargestarting switch is arranged with its main contacts normally closed andis furnished with at least an additional electrode which is connected toa point on the circuit of the discharge lamp. This point is chosen, sothat between it and one or the other of the main contact electrodesthere appears, when the supply voltage is applied to the lamp, apotentialsutficient to produce a glow discharge in the switch, such glowdischarge being suflicient to heat the heat-deformable electrode of thestartingswitch to a temperature such as to cause its-,normally closedcontacts to open. Thereupon the opening of the electrode preheatingcircuit of the lamp, the termination of the preheating period, and theinitiation of the discharge through the lamp occur.

Thus, after the normally closed contacts of the starting switch havebeen opened by the heating eiTect on the heat-deformable electrode ofthe glow discharge, so long as the discharge through the lamp persists,the voltage applied to the additional electrode is sufficient tomaintain a glow discharge and hold the contacts in the open position.When the operating voltage is removed, the starting switch contactsreclose in readiness fora further cycle of starting operations.

In some cases, for examplewhen the lamps are used on electric tractionsystems, the supply is subject to frequent interruptions. The time delaynecessary for the cycle of cooling, and subsequent reheating, of thebimetal.

electrode is an undesirable feature of a circuit arrangement using aswitch as set forth above, since the lamp remains unlighted for periodsmaterially longer than those of the interruption of supply. According toa further feature of the invention, the starting switch is modified toreduce this time delay by providing at least onefurther contact sodisposed as to be contacted in response to a further distortion of theheat-deformable electrode and thereby to enable the circuit for theheating of theelectrodes of the lamp to be completed. This furtherdistortion of the heat-deformable electrode is produced by arranging forthe supply voltage to be impressedbetween the main contacts of thestarting switch (one of which is carried by the heat-deformableelectrode) when the discharge through the lamp is absent, so that a moreintense glow is then present in the starting switch. This furtherdistortion may be produced in a shorter time periodthan would berequired-for-the necessary cooling of the heat-deformable electrode toenable the main contacts to close. On the closure of the furthercontact, theglow. in the starting switch ceases so that the reopening ofthose contacts, and the restoration of. the lamp discharge is theneffected.

We may provide in serieswith the additional electrode ofthe startingswitch a resistance (which may be constructionally integral with theswitch) the purpose of which is to limit the current in the glowdischarge from.

the additional electrode. Thus,-by adjustingthe'value of this resistanceone can vary the heatingvalue of the glow discharge and consequently thetime takenfor the contacts of the startingswitch to open.

Where we have used the term electrodeit is to be.

Fig. Line-main operating member-of theswitch consists ofa bimetalelectrode 1 which is conveniently made of U-shapedform. Thebimetal'electrode 1 is-supported by one of its limbs upon a lead-in wire2 and has the free end of its other limb arranged between contactmembers 3 and 4 supported on lead-in wires 5 and 6, respectively. Thefree end of the bimetal. electrode 1 may, and preferably does, carry acontact 7 which cooperates with the contact 4, since the main duty ofthe switch is to make and break the circuit between the contacts 4 and7. The elements of the switch are enclosed in the usual sealed glassenvelope 8, which is provided with a suitable ionizable gas filling toenable a glow discharge to take place between electrode 3 and thebimetal electrode 1 when a suitable voltage, hereinafter specified, isimpressed between them.

Referring now to the circuit diagram shown in Fig. 2, contacts 4 and 7are normally closed and are connected, respectively, to one terminal ofeach of the thermionic electrodes 9, 10 of the lamp 11, the otherterminals of the electrodes being connected to terminals 12, 13 to whichthe supply of operating current for the lamp is intended to beconnected. The lead between terminal 13 and one terminal of electrode 9includes the usual choke 14 for limiting the current flow through thelamp. The additional electrode 3 of the switch is now connected to thatterminal of the series inductance 14 which is remote from the electrode9, or to any other suitable point on the circuit as will provide, whencurrent flows through the series circuit including the electrodes 9, 10,a voltage drop sufficient to produce a glow discharge between theadditional electrode 3 and the bimetal electrode 1 of the switch.Preferably included in this connection is a resistance 15 which may, asindicated in Fig. 1, be included in the base of the starter switch, ifdesired.

On applying operating voltage to the terminals 12, 13, preheatingcurrent flows through the series circuit including the electrodes 9, 10and the contacts 7 and 4 of the starter switch, heating the electrodesof the lamp to an electron-emitting temperature. Simultaneously, a glowdischarge takes place between the bimetal electrode 1 and the electrode3 of the starter switch, which heats the electrode 1 and causes it tobend away from the contact 4. After a suitable period of time, dependingon the pressure between contacts 4 and 7, the time taken for thenecessary heating of the electrode 1, and the value of the resistor 15,the electrode 1 distorts sufliciently to open contacts 4, 7 and adischarge is produced in the usual manner between the electrodes 9, 10of the lamp as a result ofthe voltage pulse produced owing to thepresence of inductance 14 in the circuit. Thereafter, a sufiicient glowdischarge is present to maintain open the contacts 4, 7 and the contactswill only reclose in the event of the discharge through the lamp failingby reason of the removal of the operating voltage. When the operatingvoltage is restored, the above-described sequence of operations will berepeated. If, however, the discharge fails by reason of the failure ofone or other of the electrodes of the lamp, the operating voltage willstill be present between the heatdeformable electrode 1 and electrode 3of the starter switch, and consequently the contacts 4, 7 will remainopen and will not make repeated attempts to restart the lamp. Excessiveduty on the contacts 4, 7 of the starter switch is thus avoided.

If desired, an additional element 19 may be provided in the switch tolimit the travel of the free end of bimetal electrode 1 or it may bearranged that the heating effect of the glow discharge, when a dischargecurrent is passing through the lamp 11 is only sufficient to distort theelectrode 1 to a position midway between electrodes 3, 4.

Referring now to the modified form of starter switch shown in Fig. 3, inaddition to the contacts provided in the arrangement shown in Fig. 1 wehave provided an auxiliary fixed contact 17 located between the mainfixed contact 4 and the fixed electrode 3 and electrically connectedwith the main fixed contact 4. We furthermore provide an auxiliarymovable contact 18 attached to the bimetal electrode 1. This movablecontact is so arranged, between the fixed contact 17 and fixed electrode3, that, when the bimetal electrode 1 distorts sufiiciently to carry themain movable contact 7 into engagement with the fixed contact 17, theauxiliary movable contact 18 will simultaneously engage the fixedelectrode 3. This modified form of starter switch is particularlysuitable for use in circuits where the supply is subject to momentaryinterruptions of sufficient duration to prevent immediate restriking ofthe discharge across the lamp. Under these conditions, when thedischarge through the lamp momen-' tarily ceases owing to interruptionin the supply, and the supply is thereafter reconnected, due to thepresence of the supply voltage between auxiliary fixed contact 17 andthe bimetal electrode 1, a more intense glow takes place with the resultthat a further bending of the bimetal electrode 1 occurs. It will, ofcourse, be understood that the reconnection of the supply, mentionedabove, occurs before the glow switch has time to cool sufficiently torestore bimetal electrode 1 to its rest position, wherein it is incontact with electrode 4. The bending which now occurs, as a result ofthis more intense glow, elfects mutual engagement of contacts 7, 17 and18, 3. The electrode heating circuit of the lamp is thereupon completed,and, as a result of the consequent removal of the glow discharge, thebimetal electrode 1 cools, opening the circuit at the contacts 18, 3 and17, 7. The discharge through the lamp is thereby re-initiated and thebimetal electrode is once more heated by the glow discharge betweenfixed electrode 3 and auxiliary movable contact 18. This heating is justsufficient to maintain the main movable contact 7 in a position midwaybetween fixed contacts 17 and 4. The normal running position of theswitch is thereby restored.

Fig. 4 shows a further arrangement, similar in character to that shownin Fig. 3, but in which the fixed electrode 3 and auxiliary fixedcontact 17 are arranged to be simultaneously interconnected by a contactelement 7 in the form of a transverse wire located on the free end ofthe bimetal element 1.

The adjustment of the duration of the preheating period for the lampelectrodes may be effected by varying the value of the series resistance15. An increase in the value of the resistance will diminish the glowdischarge current, and therefore increase the period of time requiredfor distorting the heat-deformable electrode 1 and effecting opening ofcontacts 4, 7.

We preferably connect a radio interference suppression condenser 16 inshunt with the contacts 4, 7 of the starter switch.

While certain specific embodiments have been shown and described, itwill, of course, be understood that various modifications may be madewithout departing from the invention. The appended claims are,therefore, intended to cover any such modifications coming within thetrue spirit and scope of the invention.

What we claim as new and desire to secure by Letters Patent of theUnited States is:

1. In combination, an electric discharge device having two cooperatingelectrodes at least one of which is thermionic; a ballast impedanceconnected in series with said discharge device in an operating circuittherefor and proportioned to limit the discharge current therethrough; athermal glow discharge starting switch comprising a sealed envelopecontaining an ionizable medium, a pair of normally closed maincontacting electrodes at least one of which is heat deformable anddesigned to break contact when heated, and an auxiliary electrodeadjacent said heat-deformable main electrode and defining therewith aglow discharge gap; the main electrodes of said switch being connectedacross the electrodes of said discharge device in a preheating circuitshunting said discharge device and serially including its thermionicelectrode; and a connection between the side of said ballast impedanceremoved from said discharge device and said auxiliary electrode.

2. In combination, an electric discharge device having two cooperatingelectrodes at least one of which is thermionic; a ballast impedanceconnected in series with said discharge device in an operating circuittherefor and proportioned to limit the discharge current therethrough; athermal glow discharge starting switch comprising a sealed envelopecontaining an ionizable medium, a pair of normally closed maincontacting electrodes at least one of which is heat deformable anddesigned to break contact when heated, and an auxiliary electrodeadjacent said heat-deformable main electrode and defining therewith aglowdischarge gap; the main electrodes of said switch being connectedacross the electrodes of said discharge device in a preheating circuitshunting said discharge device and serially including its thermionicelectrode; and a resistanceconnecting said auxiliary thermal switchelectrode to the sideof said ballast impedance removed from saiddischarge device.

3. In combination, an electric discharge device having two cooperatingelectrodes at least one of which is therm-' ionic; a voltage supply; aballasting impedance connected in series with said discharge deviceacross said supply to constitute a main discharge circuit during normaloperation of said device; a thermal glow discharge starting switchcomprising a sealed envelope containing an ionizable medium, a pair ofnormally closed main contacting electrodes at least one of which is heatdeformable and designed to break contact when heated, and an auxiliaryelectrode adjacent to said heat-deformable main electrode and definingtherewith a glow discharge gap; the main electrodes of said dischargedevice being connected in a preheating circuit shunting said dischargedevice and serially including its thermionic electrode; and a connectionbetween said auxiliary thermal switch electrode and the side of saidsupply connected to said ballasting impedance in order to produce adischarge in said gap for causing said heat deformable main electrode tobreak contact with the other main electrode of said switch.

4. In combination, an electric discharge device having a pair ofcooperating electrodes of the filamentary thermionic type; a voltagesupply; a ballasting impedance connected in series with said dischargedevice across said supply to constitute a main discharge circuit duringnormal operation of said device; a thermal glow discharge startingswitch comprising a sealed envelope containing an ionizable medium and apair of normally engaged and closed main contacting electrodes, at leastone of which is heat deformable and designed to disengage and breakcontact when heated, and an auxiliary electrode spaced apart from saidheat deformable electrode and defining therewith a glow discharge gaptherebetween; the main electrodes of said switch being connected acrossthe thermionic electrodes of said discharge device in a preheatingcircuit shunting said discharge device and serially including saidthermionic electrodes; and a connection between said auxiliary electrodeand the side of said supply connected to said ballastin impedance inorder to produce a discharge in said gap for causing said heatdeformable main electrode to break contact with the other main electrodeof said switch.

5. In combination, an electric discharge device having a pair ofcooperating electrodes of the filamentary thermionic type; a voltagesupply; a ballasting impedance connected in series with said dischargedevice across said supply to constitute a main discharge circuit duringnormal operation of said device; a thermal glow discharge switchcomprising a sealed envelope containing an ionizable medium, a mainfixed contacting electrode, a heatdeformable contacting electrodenormally biased into engagement with said main fixed contactingelectrode but movable away therefrom when heated, an auxiliary electrodeadjacent to said heat-deformable electrode and defining therewith a glowdischarge gap, and an additional contact on said main fixed contactingelectrode engageable simultaneously with said auxiliary electrode by aportion of said heat deformable electrode at the limit of movementthereof; the contacting electrodes of said switch being connected acrossthe electrodes of said discharge device in a preheating circuit shuntingsaid discharge device and serially including its electrodes; and aconnection between said auxiliary fixed electrode and the side of saidsupply connected to said ballasting impedance in order to produce,during normal operation of said discharge device, a glow dischargebetween said auxiliary electrode and said heat-deformable electrodewithin said switch.

6. A thermal glow discharge switch comprising a sealed envelopecontaining an ionizable medium, a main fixed contacting electrode, aheat-deformable contacting electrode normally biased into engagementwith said main electrode but movable away therefrom when heated, anauxiliary fixed electrode spaced from a portion of said heat-deformableelectrode for defining a glow discharge gap therebetween and located inthe path of movement of said portion, and an additional fixed contactelectrically connected to said main electrode and spaced from saidheat-deformable electrode but in the path of movement thereof, so as tobe engaged thereby simultaneously with the engagement of said auxiliaryfixed electrode by said portion.

7. A thermal glow discharge switch comprising a sealed envelopecontaining an ionizable medium, a main fixed contact and an additionalfixed contact spaced apart but electrically connected together on acommon fixed electrode, an auxiliary fixed electrode spaced apart fromsaid fixed contacts, a heat-deformable electrode carrying a main movablecontact and an additional movable contact, said main movable contactnormally engaging said main fixed contact, said additional movablecontact being spaced between said additional fixed contact and saidauxiliary fixed electrode to provide a glow discharge gap between itselfand said auxiliary fixed electrode, said heatdeforrnable electrode beingoperable, when heated by a glow discharge between said main fixedcontact and said main movable contact, to position said main movablecontact substantially midway between said main and additional fixedcontacts, and said heat-deformable electrode being further operable,when heated by an additional glow discharge between said additionalmovable contact and said auxiliary fixed electrode, so that said mainmovable contact engages said additional fixed contact and saidadditional movable contact simultaneously engages said auxiliary fixedelectrode.

8. A thermal glow discharge switch comprising a sealed envelopecontaining an ionizable medium, a main fixed contact and an additionalfixed contact spaced apart and electrically connected together on acommon electrode, an auxiliary fixed electrode spaced apart inside-by-side relationship with said additional fixed contact, aheat-deformable electrode having its free end normally biased intoengagement with said main fixed contact and spaced apart from saidauxiliary fixed electrode for defining a glow discharge gaptherebetween, said heat-deformable electrode being operable, when heatedby a glow discharge, to move said free end out of engagement with saidmain fixed contact to a position intermediate said main fixed contactand said auxiliary fixed electrode, and said heat-deformable electrodebeing further operable, when heated by an auxiliary glow dischargebetween said auxiliary fixed electrode and itself, to move said free endfurther in order to form electrical contact simultaneously with saidauxiliary fixed electrode and said additional fixed electrode.

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